Application of large area avalanche photodiodes for alpha liquid scintillation counting

In order to improve the resolution in alpha liquid scintillation and to promote this method for the measurement of actinides in environment, a silicon Large Area Avalanche Photodiode (LAAPD) has been tested as liquid scintillation detector. The set-up consists of a LAAPD (16 mm diameter) coupled to a thin vial containing alpha-emitters and a liquid scintillation cocktail. After optimization of several parameters like bias voltage, temperatures, counting geometry and composition of scintillating cocktail, energy resolutions are found to be better than those obtained with photomultiplier tubes: 5% (200 keV FWHM) for 232Th and 3.9% (260 keV FWHM) for 216Po. The improvement in energy resolution is not due to higher quantum efficiency of the silicon device but to better uniformity of the spatial photoresponse. A few energy spectra of thorium, plutonium and americium are given as example.